Fix full screen button not supported

core/modules/startup/rootwidget.js

@@ -67,14 +67,15 @@ exports.startup = function() {
 		});
 	});
 	var fullscreen = $tw.utils.getFullScreenApis();
-	$tw.rootWidget.addEventListener("tw-full-screen",function(event) {
-		if(document[fullscreen._fullscreenElement]) {
-			document[fullscreen._exitFullscreen]();
-		} else {
-			document.documentElement[fullscreen._requestFullscreen](Element.ALLOW_KEYBOARD_INPUT);
-		}
-	});
-
+	if(fullscreen) {
+		$tw.rootWidget.addEventListener("tw-full-screen",function(event) {
+			if(document[fullscreen._fullscreenElement]) {
+				document[fullscreen._exitFullscreen]();
+			} else {
+				document.documentElement[fullscreen._requestFullscreen](Element.ALLOW_KEYBOARD_INPUT);
+			}
+		});
+	}
 	// If we're being viewed on a data: URI then give instructions for how to save
 	if(document.location.protocol === "data:") {
 		$tw.rootWidget.dispatchEvent({

core/modules/utils/dom/browser.js

@@ -135,8 +135,8 @@ Return the names of the fullscreen APIs
 */
 exports.getFullScreenApis = function() {
 	var d = document,
-		db = d.body;
-	return {
+		db = d.body,
+		result = {
 		"_requestFullscreen": db.webkitRequestFullscreen !== undefined ? "webkitRequestFullscreen" :
 							db.mozRequestFullScreen !== undefined ? "mozRequestFullScreen" :
 							db.msRequestFullscreen !== undefined ? "msRequestFullscreen" :
@@ -150,6 +150,11 @@ exports.getFullScreenApis = function() {
 							d.msFullscreenElement !== undefined ? "msFullscreenElement" :
 							d.fullscreenElement !== undefined ? "fullscreenElement" : ""
 	};
+	if(!result._requestFullscreen || !result._exitFullscreen || !result._fullscreenElement) {
+		return null;
+	} else {
+		return result;
+	}
 };
 
 })();